1. Field of the Invention
This invention relates to apparatus for generating high frequency signal bursts and is more particularly concerned with such apparatus which includes adjustable control circuitry for providing a variable crest factor of the output power, one application of such apparatus being in the field of electrosurgery.
2. Description of the Prior Art
It is well known in the art to apply high frequency energy, RF signals and the like, to cut, cauterize, dessicate and/or coagulate body tissues and fluids. Basically, it is matter of the molecules of these elements being able to respond, or not respond, to polarity reversals with the result that tissue, depending on the particular application, ruptures, burns, or in the case of fluids such as blood coagulates.
Many devices have been devised for applying high frequency energy to electrosurgical handpieces, including apparatus for generating and applying continuous waves, apparatus for generating burst of high frequency energy, and apparatus for chopping continuous waves during application to an electrosurgical instrument. Over the last few years, it has been determined that the ratio of the peak voltage of the output wave of a power oscillator to the root mean square of the output voltage, hereinafter called the "crest factor", is a parameter which affects, for example, cutting and coagulation. A low crest factor, e.g. 1.4, will effect cutting; and as the crest factor increases, coagulation is obtained without cutting.
Attempts have been made to obtain different crest factors in a single apparatus by generating burst of energy having changing envelopes, such as a decaying waveform. While these have proven somewhat satisfactory, the art has not heretofore provided an apparatus capable of having a continuously adjustable crest factor, particularly a crest factor which is variable over substantially an entire half wave with respect to the supply voltage of a power oscillator except by relatively expensive pulse modulation techniques.